This invention relates to a simulation for reproducing an interesting phenomenon on a computer, in particular, a spatial simulation program and system for updating a variable in a numerical grid for each time step.
Recently, for the purpose of grasping an interesting phenomenon, a system for easily realizing a spatial simulation on a standard computer such as a PC (Personal Computer) has been a focus of attention. In general, in the spatial simulation, a real space is represented by a plurality of numerical grids, and a phenomenon to be simulated is represented by a variable. Furthermore, a time-based change in the phenomenon is represented by updating the variable for each certain duration (time step). For example, a flood simulation which is a kind of the spatial simulation is known, for example, as described in “Manual for economic survey of flood control (draft)”, published by River Bureau, Ministry of Construction, May 1999, pages 26 to 36. The flood simulation represents flood by updating variables such as water depth, current velocity, etc.
The flood simulation supposes principally the case where a levee failure happens, and calculates a water depth in the flooded area. First, prior to the start of the simulation, an area to be simulated (target area) is determined. The area that does not correspond to the target area cannot be taken into consideration in the simulation. Next, the arrangement of numerical grids in the target area is determined. In order to allow the currently existing PC to execute a processing within a practical time, the number of numerical grids is required to be limited to 10,000 or less. Therefore, the numerical grid is formed as a square shape, about 250 m on a side. Finally, variables such as a water depth and a current velocity in the numerical grids arranged in the target area are updated for each time step.